The present invention relates to a process for producing (1R,3R,6R)-6-dimethylaminomethyl-1-(3-methoxyphenyl)-cyclohexane-1,3-diol or (1S,3S,6S)-6-dimethylaminomethyl-1-(3-methoxyphenyl)-cyclohexane-1,3-diol or mixtures thereof.
U.S. Pat. No. 5,733,936 (=EP 753,506) discloses 6-dimethylaminomethyl-1-(3-hydroxy- or 3-C1-C4-alkoxyphenyl)-cyclohexane-1,3-diols which are suitable for use as pharmacologically effective analgesics for the treatment of pain. These compounds are chiral and have 3 asymmetric carbon atoms. These 6-dimethylaminomethyl-1-(3-hydroxy- or 3-C1-C4-alkoxyphenyl)-cyclohexane-1,3-diols are produced in a multi-step process by means of a protecting group strategy (introduction and splitting of ketal groups) and subsequent hydrogenation.
It has been found that some stereoisomers are characterized by particularly good pharmacological efficacy. These stereoisomers are the (1R,3R,6R)- and (1S,3S,6S)-stereoisomers of formulas (Va) and (Vb) or mixtures thereof:

The (1R,3R,6R)- and (1S,3S,6S)-stereoisomers of formulas (Vc) and (Vd)
are, in contrast, less desirable and their formation should thus be avoided as far as possible during the production process.